The present invention is directed to a method and apparatus for converting capacitance in a capacitive sensor to voltage.
In a capacitive sensor, the capacitance of one or more capacitors varies with variations of a physical parameter that is being monitored. Many different types of capacitive sensors are known, and many such sensors have been used to monitor and measure various types of physical parameters. An example of such a capacitive sensor is a microelectro mechanical system (xe2x80x9cMEMSxe2x80x9d), which may be used to sense acceleration. A typical MEMS sensor comprises one or more small capacitors etched into a piece of silicon. One plate of a MEMS capacitor is fixed and the other plate is moveable. Acceleration of the sensor causes the moveable plate to move, changing the capacitance of the capacitor. The amount of movementxe2x80x94and hence the change in capacitancexe2x80x94is proportional to the amount of acceleration.
Regardless of the type of capacitive sensor or the physical parameter being sensed, generally speaking, the variations in capacitance must be converted into a voltage signal before meaningful use can be made of the output of the sensor. The present invention is directed to a method and apparatus for converting capacitance into voltage. Although a MEMS sensor is mentioned above, the present invention is not limited to use with a MEMS sensor. Rather, the present invention may be used with any type of capacitive sensor.
The instant invention is directed to a method and apparatus for converting variations in capacitance in a capacitive sensor into a voltage signal. A capacitive sensor monitors a physical parameter, and a capacitance of the sensor varies with the physical parameter. An alternating voltage is applied to the capacitive sensor, which creates an output signal. The output signal is modulated to produce a voltage signal. The modulated signal is a voltage signal that corresponds to the capacitance of the sensor.